Electron discharge apparatus



May 15, 1956 c. c. EAGLESFIELD ELECTRON DISCHARGE APPARATUS Filed Dec. 2, 1952 VOlTAGE (HT! #HTZ) VOLTAGE SUPPLY HTS VOLTAGE SUPPLY HTS VOLTAEIE SUPPLY HTZ SUPPLY HT I V0 LTA CIE VOLTAGE SUPPLY HT4 CHT4 me Inventor C. C. EAGLESFIELD A ltorney nited States Patent ELECTRON DISCHARGE APPARATUS Charles Cecil Eaglesfield, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application December 2, 1952, Serial No. 323,562

2 Claims. (Cl. 250-27) The present invention relates to electric circuit arrangements for reducing microphonicity which is due to movement of electrodes in associated electron discharge devices.

If a low noise circuit be required, it is to be assumed that as far as possible the associated electron discharge devices will be designed to avoid looseness of parts Where they fit together: for example, steps would be taken to ensure that the cathode fitted firmly in its locating insulators. Microphonicity which nevertheless arises in such a circuit will be caused not by rattling of parts but by vibrational movements.

For such movements to cause microphonicity, the movement of the electrodes has to be such as to cause a change of current to one of the valve electrodes, and, therefore, movements which cause a change of clearance between electrodes are important. Thus in a conventional radio valve construction in which a cylindrical cathode is surrounded by an elliptical helical control grid which in turn is surrounded by an anode and possibly intermediate grids, movement causing the greatest change of current to the anode or to intermediate grids is normally along the minor axis of the grid. For the moment we may confine our attention to such movement.

If there were exact symmetry of the electrodes along the minor axis, a movement, for example of the cathode towards one side of the grid, would increase the current in that direction, by exactly the amount it would decrease the current in the opposite direction. The movement would therefore cause no total current change-provided the movement is smallwhich in practice is always the case. Thus, if the device had exact symmetry to either side of the major axis, movement along the minor axis would not produce microphonicity. A similar argument applies to movement along any other axis of the device.

In practice however, it is impossible to provide exact symmetry of electrodes in an electron discharge device with respect to any given axis. Vibration of the structure will cause flexion of one or more electrodes, which then is evident in the circuit as microphonicity.

i have found that microphonicity due to vibratory flexion of an electrode in a structure which is only approximately symmetrical about a given axis, may be compensated by airanging that the current to either side of the s..id axis is separately controlled. This may be done by providing the discharge device with one or more auxiliary electrodes or by sub-dividing one of the electrodes, such as the anode, into two parts for D. C. purposes.

According to the present invention, therefore, there is provided an electric circuit arrangement comprising an electron discharge device an electrode of which is subject to vibratory fiem'on giving rise to microphonicity which would not occur but for the asymmetrical assembly of the electrodes of the said device with respect to a given axis, characterised in this that the said electrodes are adapted and bias means are provided for producing a distribution of electron flow counteracting the effect of the said asymmetry on the flow distribution otherwise obtained.

ice

Embodiments of the invention provide an electric circuit arrangement comprising an electron discharge device having a cathode, at least one grid positioned on opposite sides of, as by surrounding, the said cathode and an anode on each said opposite side, the said electrodes being only approximately symmetrical in position with respect to the said cathode; electrode means, such as the sub-division of the said anode into separate portions and corresponding bias means producing electron flow to either said side compensating for departure from symmetry of the electrode positions, whereby microphonicity due to vibrational fiexion of electrodes is reduced.

Embodiments of the invention will be described with reference to the accompanying drawings in which:

Fig. l is a schematic diagram of an arrangement according to the invention utilising a triode valve and,

Fig. 2 shows a cross section through a triode valve adapted for use with other arrangements according to the invention.

In Fig. 1 there is shown diagrammatically at 1 a plan view of a triode valve, comprising a cathode 2, a surrounding elliptical control grid 3 mounted on support rods 4 and 5 and an anode comprised of the segments 6 and 7 at either end of the minor axis of the grid 3. For present purposes We may assume that the triode is to be used in an audiofrequency resistance-capacitance amplifier circuit. The two anode segments 6 and 7 are connected in parallel for signal purposes by the capacitor 8 but are shown connected to different anode supply potentials HTl and HTZ, through separate resistors 9 and 10. Each anode segment is connected for signal purposes to a common output terminal 11 through D. C. blocking capacitors 12 and 13 respectively. Circuit connections to the other electrodes may follow any known arrangement with which we are not here concerned and which therefore has not been shown on the drawing.

If, now, it be assumed that the major axis of grid 3 is slightly to the right of the axis of cathode 2 which is normal to the plane of the drawing, then if both anode segments 6 and 7 are provided with the same HT supply, the mutual conductance of the anode-cathode path including anode segment 6 would be greater than that including the anode segment 7. Consequently, if cathode 2 vibrates so as to flex to either side of the static vertical axis, an oscillatory potential will be induced in the connections to each of the anode segments, but these potentials will be out of phase with one another. Due to the higher mutual conductance of the anode segment 6 portion of the circuit however, complete cancellation will not occur, and a signal will appear between terminal 11 and the cathode, having a frequency that of the period of vibration of cathode 2; i. e. microphonic noise is pro duced. In applying the invention however, under the circumstances postulated above, the voltage supplied to terminal HTl will be slightly greater than that of terminal HTZ, so changing the relative mutual conductances of the two valve portions that the induced microphonic voltages may cancel out in spite of the asymmetry of the electrode system.

If desired, instead of splitting the anode into two segments 6 and 7, an additional electrode could be mounted within the tube 1 so as to draw more current from the cathode to one side to compensate for the asymmetry of electrode mounting. However, the provision of a split anode is probably the simplest solution in the triode case.

In a tube such as illustrated in Fig. l, microphonicity is most likely to arise due to asymmetry along the minor axis. If, in addition, it be required to compensate for asymmetry along the major axis of the grid, a tube construction such as illustrated diagrammatically in Fig. 2 may be applied with appropriate circuit connections analogous to those adopted in Fig. l.

and 18 to the other side. '18 are connected to different anode supply potentials In Fig. 2 the tube 14 comprises a cathode 2 and a grid 3 as in the tube of Fig. 1, but the anode is now split into four segments 15, 16, 17 and 18, segments 15 and 17 lying to one side of the minor axis and segments 16 The anode segments 15 HT3 HT6, respectively, the supply HT 3 being unequal to the supply HTS and the supply HT4 being unequal to the supply HT6. Similarly, if it be required also to apply the invention to counteract the afiect of asymmetry along the cathode axis perpendicular to the plane of the drawing, the anode could further be sub-divided into tical purposes.

When the invention is applied to circuits containing tetrodes or pentodes, since the anode voltage usually has little effect on the anode current in these tubes, it is preferable to sub-divide the accelerating or screen grid which has a much larger effect on the anode current. Alternatively, in a tetrode, sub-divided beam forming plates may be used to influence the electron flow along the desired axis of the control grid in different measures on the respective opposite sides of the cathode.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made by way of example and not as a limitation on the scope of the invention.

What I claim is:

1. An electric circuit arrangement comprising an electron discharge device having a plurality of electrodes including a cathode, at least one grid positioned on opposite sides of the said cathode, and an anode extending on said opposite sides, the said electrodes being only approximately symmetrical in position with respect to the said cathode, one of said electrodes other than the cathode having separate portions on each of said sides, and bias means, controlling electron flow, applying different voltages to each side of said one electrode to compensate for departure from symmetry of the electrode positions, Whereby microphonicity due to vibratory flexion of electrodes is reduced.

2. An electric circuit arrangement according to claim 1 in which the said discharge device is a triode valve having an elongated cathode, and elliptical control grid surrounding the cathode and a pair of anode segments, one on either side of the major axis of the grid and in which said bias means includes means for applying separate anode direct current voltages to said anode segments, means electrically coupling said segments at the signal frequencies but separating them at direct current voltages.

References Cited in the file of this patent UNITED STATES PATENTS 1,280,769 Langmuir Oct. 8, 1918 1,329,283 Arnold Jan. 27, 1920 1,366,411 Nicolson Ian. 25, 1921 1,596,198 Loewe Aug. 17, 1926 1,630,753 Massolle et al May 31, 1927 2,265,311 Preisach et al. Dec. 9, 1941 2,528,437 Joy Oct. 31, 1950 2,547,107 Anderson Apr. 3, 1951 

